This is a prospective study of provider attitudes and patient outcomes regarding adherence and the risk of resistance to antiretroviral therapy in homeless and marginally housed (H/M) people with HIV infection. Advances in ARV therapy with protease inhibitor containing regimens has dramatically impacted HIV-related morbidity and mortality. However, the appropriate use of these therapies in populations with high rates of chemical dependency and mental illness, such as the H/M, is unclear due to concerns of nonadherence and the selection of resistant virus. In the proposed study, face-to-face interviews will be conducted with a representative sample of providers who deliver medical care to HIV-infected H/M people in San Francisco. Providers will be identified from those who deliver medical care to participants in the REACH cohort, which is a systematic representative sample of H/M HIV-infected people obtained from lunch lines, shelters, and low income single room occupancy (SRO) hotels. The interview will assess each provider's decisions regarding the initiation or deferral of antiretroviral therapy for that provider's patient(s) in the REACH Cohort. These data will then be compared with patient-derived measures of ARV adherence, viral load suppression and the incidence of resistance-associated mutations. The comparison of provider and patient-derived measures aim to determine the accuracy of provider estimations of adherence and the risk of developing ARV resistance in this population. This information aims to improve understanding how ARV therapy is delivered to this growing segment of the HIV epidemic.